Pancreatic carcinoma usually presents at an incurable stage. The precursor is the pancreatic intraepithelial neoplasm (PanIN), occurring in up to 60 percent of the older population. Only a small subset is histologically advanced and progresses to invasive cancer. Invasion induces an exuberant host: tumor interaction that remains poorly understood, but is likely to have fundament influences on tumor biology and distant host organs. Therefore, pancreatic carcinogenesis is now understood as a progression of intraepithelial neoplasia and as an interaction of cellular compartments. During the past seven years of this SPORE project, we defined a progression of alterations in the K-ras, p16, DPC4/SMAD4, Her2/neu, and BRCA2 genes in the precursor lesions. Variant tumor types were re-interpreted within this tumorigenic model and we comprehensively profiled gene expression through SAGE analysis. A progression model of neoplasia was constructed, contributing to a new consensus classification system for PanIN lesions. Our long-term goal is to identify the fundamental genetic alterations and patterns of gene expression in the progression of precursor lesions to invasive carcinoma, in order to guide diagnosis and therapy. In the proposed grant period, we will: 1) Determine the frequencies and relative timing of genetic and other alterations along the histologic stages of PanIN. We will apply techniques that have proven efficient in this effort, including the microdissection of lesions for genetic analysis and the use of immunohistochemistry. 2) Construct SAGE profiles of pancreatic cancer cell lines and primary tumors. This is the foundation for identification of stage- and tissue-specific markers and insights into host: tumor interactions. 3) Delineate the architectural compartments of gene expression in the host:tumor interaction. Genes identified in Aim 2 are parsed into cellular compartments using in situ and experimental techniques. 4) Develop the new markers in expanded translational settings, such as difficult biopsies, studies applied to Aim 1, variant tumor types, and serum.